Visible-Light-Promoted [4π + 2σ] Annulation of Dienes and Alkylamines via Dual Inert C(sp3)-H Bond Activation.

Abstract

Herein, visible-light-promoted [4π + 2σ] annulation of dienes and alkylamines was achieved via dual C(sp3)-H bond functionalization of alkylamines. The elusive enamine precursors are generated under mild conditions by photoredox catalysis, efficiently annulated by the diene, and simultaneously functionalized with two aliphatic C(sp3)-H bonds, resulting in the productive synthesis of new aromatic rings. The aromatic ring construction provides direct access to 2-hydroxybenzophenone derivatives in high yields (up to 90%). This [4π + 2σ] annulation reaction demonstrates mild reaction conditions, high reaction efficiency, and broad functional group tolerance, and this synthetic protocol has been made available for the late-stage transformation of natural products and commercial drugs.